Giant ice spider
It is unclear if they are giant spiders who live in ice-filled frozen wastes, or if they are magical constructs made of living ice, like the mythical Ice dragon.
A Game of Thrones
A Storm of Swords
A Feast For Crows
The horn blew thrice long, three long blasts means Others. The white walkers of the wood, the cold shadows, the monsters of the tales that made him squeak and tremble as a boy, riding their giant ice-spiders, hungry for blood ...—thoughts of Samwell Tarly